Concrete Footing Calculator
For continuous footings (footers) under walls, and rectangular pad footings. Enter the length in feet and the width and depth in inches.
Concrete needed
0.72 cubic yards
19.6 ft³ · 0.55 m³ · includes 10% extra
You need about 0.72 cubic yards of concrete, or 33 bags of 80 lb mix.
Bags of premix
- 6640 lb bags
- 5350 lb bags
- 4460 lb bags
- 3380 lb bags
- —20 kg bags
- —25 kg bags
- Before extra0.66 yd³ (17.8 ft³)
- Weight of bags2,640 lb
- Per hole—
- Ready-mix costAdd a price per yd³
- Bagged costAdd a price per bag
One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.
At 0.72 yd³ (33 × 80 lb bags, 2,640 lb), bags and a small ready-mix load are both reasonable. Ask local suppliers for their minimum load and short-load fee before deciding.
Estimate only, not a quote or engineering advice. Disclaimer
How footing volume is calculated
A continuous footing is a long rectangular block, so its volume is length × width × depth. Because footing width and depth are usually given in inches, convert both to feet (divide by 12) first.
Example: a 40 ft footing 16 inches wide and 8 inches deep is 40 × 1.333 × 0.667 = 35.6 ft³, or 1.32 yd³. With 10% extra, order about 1.45 yd³.
Concrete per 10 feet of footing
| Width × depth | ft³ | yd³ | Feet per yd³ | 80-lb bags |
|---|---|---|---|---|
| 12 × 6 in | 5.00 | 0.185 | 54 | 9 |
| 16 × 8 in | 8.89 | 0.329 | 30 | 15 |
| 20 × 10 in | 13.89 | 0.514 | 19 | 24 |
| 24 × 12 in | 20.00 | 0.741 | 14 | 34 |
Perimeter footings
For a footing that runs around a building, use the total length of footing measured along its center line. For a rectangle, that is about 2 × (length + width) minus 4 × the footing width, so the corners aren't counted twice. Set "Number of footings" for repeated pad footings of the same size, such as under deck or porch posts.
Size and code
Footing width and depth depend on the load, the soil and the frost depth where you live. This calculator only works out quantity. Your local building department, plans or engineer set the actual size.
Frequently asked questions
How much concrete do I need for a footing?
Multiply length (ft) by width and depth (both in feet). A 20 ft footing that is 16 × 8 inches holds 17.8 ft³, which is 0.66 yd³, or 0.72 yd³ with 10% extra.
Is a footer the same as a footing?
Yes. Footer and footing both mean the wide concrete base that spreads a wall’s or post’s load into the soil. The math is the same.
How many bags of concrete for a footing?
Find the cubic feet and divide by the bag yield: 0.60 ft³ for an 80-lb bag, 0.45 ft³ for 60 lb. A footing of 17.8 ft³ plus 10% needs 33 bags of 80-lb mix.
Do I include the rebar in the volume?
No. Rebar takes up a tiny share of a footing’s volume, and the waste allowance more than covers it.
Related
Sources
- QUIKRETE: Concrete Mix No. 1101 data sheet (Revised Oct 2022; checked Nov 11, 2026)